This invention concerns axial flow rotary separators of the type used principally in combine harvesters and particularly the feeding of separators in which the rotor includes axially displaceable crop engaging elements.
Although the long history of threshing and separating of agricultural grain crops has been dominated by the conventional arrangement of transverse threshing cylinder upstream of a rack or straw walkers, there have also been attempts, spanning many years, to develop axial flow rotary separation. In recent years, combine harvesters embodying this principle have captured a significant portion of the market.
Until the recent disclosure of Witzel (U.S. Pat. No. 4,408,618), all known axial flow rotary separators with driven rotors depended for axial indexing on relative motion or slippage between the crop material and angled surfaces within the separator such as angled blades on the rotor or helical guide vanes on the casing or a combination of the two. Ideally, in such separators, the crop material is deflected along the generally radially extending surfaces of the blades or guide vanes but, inevitably there is some radially outward migration of material into the annular clearance space between rotor extremities and casing. Overall, there are very high friction losses, specific power consumption is high and handling of some types of material is unreliable. For example, in damp material, there may be a tendency to "roping" of the material, leading to plugging of the separator.
Nusser (U.S. Pat. No. 4,178,942) has proposed a modification of the conventional axial flow rotary separator, substituting more or less randomly oscillating tines for the fixed crop engaging elements of conventional rotors and relying entirely on helical guide vanes for axial propulsion. The intermittently engaging, positively propelling and "spirally moving" crop-engaging elements of Witzel's rotor makes guide vanes unnecessary and dramatically cuts the specific power requirement while improving material handling characteristics and maintaining an acceptable level of separating efficiency.
The feeding of axial flow rotary separators presents special difficulties especially when the direction of flow of the delivered material is generally parallel to the rotor axis. A flow of material moving generally linearly and converging on the rotor axis must be engaged by the rotor and transformed into an annular mat moving spirally downstream in the annular space between rotor and casing. The separating (and threshing when included) function depends on fairly high rotational speed in the rotor so that obviously a simple rotor tends to repel, centrifugally, material offered to it. The patent literature of recent years presents abundant evidence of this problem and the attempts to overcome it. In general, the feed and/or transition portions of separator rotors have relied on a screw conveyor-like form and abruptly tapering and confining housings to force incoming material through the transition from linear stream to spirally moving annular mat. Tangential feeding (as in U.S. Pats. No. 3,315,449 Morrison or U.S. Pat. No. 4,180,081 Shaver for example) may be smoother but the tangential configuration is not always convenient and its efficiency is still subject to the limitations of the fixed element rotor. (Tangential feeding may be convenient or appropriate in dual rotor machines where side-by-side rotors share a common housing and are driven in the same direction, as disclosed for example in Russian patent No. 219 311 and U.S. Pat. No. 4,367,757, Claas).
The screw conveyor form of feed rotor is also and typically used in twin side-by-side or dual rotor separators of the type where, beyond the infeed portion, each rotor operates independently, in its own casing. In general purpose combines with separators designed to handle a wide range of crops, including small grains and corn, the material handling characteristics of the feed rotor forms employed (fixed element) and the need to divide the flow as evenly as possible between the two rotors has dictated that the rotors be contrarotating and that their direction of rotation be such as to repel incoming material directed towards the space between the rotors. The incoming stream is divided therefore and diverted laterally outwards and typically upwards into the infeed housing and the beginning of the annular space between rotor and casing. This method of flow-dividing is imprecise and inefficient even when supplemented by upstream dividing elements such as "knives" in the combine feeder house (see for example U.S. Pat. No. 3,794,046 Muijs and U.S. Pat. No. 3,794,047 DeCoene).
In some known twin rotor corn shellers embodied in self-propelled harvesters, direction of rotation is opposite to that just described so that material directed to the space between the rotors and satisfactorily engaged is drawn between the rotors rather than repelled (see U.S. Pat. No. 3,536,077 Stott). This arrangement may be satisfactory in a single crop machine such as the self-propelled corn harvester/sheller where it is feasible to gravity feed the rotors and the physical nature of the crop does not require high rotor speed or a particularly agressive rotor feed portion
Witzel's disclosure (U.S. Pat. No. 4,408,618) is directed almost exclusively to the structure and function of his rotor as a separating rotor, successful feeding of the separator having been assumed. Witzel comments that a rotor with crop material engaging elements according to his inventive principle might function well in a separator feed section but he makes no specific suggestions for configuration or arrangement of the feed section.